Please double check you (3ds Max) can access the optmat.mse file located at C:\Program Files\Autodesk\3ds Max 2016\scripts\forestpack (or the corresponding ...\scripts\forestpack folder if you changed the default 3ds Max location).
Regarding the XRef Object Merge: Units Mismatch warning window: Because of the importation process slightly changed, that message is triggered while working with the 3ds Max 2016 (even it's actually merging items/models and not linking them as XRefs). Anyway, upon our testing it behaves correctly (when using any geometry from scene with different Scene Unit Setup it´ll rescale the geometry accordingly). I would suggest you always leave the default option Rescale the XRef Objects to the System Unit Scale marked.
We've already contacted Autodesk regarding it, but it doesn't seem there is a possibility to avoid that "confirmation" step.